The flight is part of the Hyper-X program, a research effort designed to demonstrate alternate propulsion technologies for access to space and high-speed flight within the atmosphere. It will provide unique "first time" free flight data on hypersonic air-breathing engine technologies that have large potential pay-offs.

Hyper-X is inherently a high-risk program. No vehicle has ever flown at hypersonic speeds powered by an air-breathing scramjet engine. In addition, the rocket boost and subsequent separation from the rocket to get to the scramjet test condition have complex elements that must work properly for the mission to be successful.

The $250 million program began with conceptual design and scramjet engine wind tunnel work in 1996. In a scramjet (supersonic-combustion ramjet), the flow of air through the engine remains supersonic, or greater than the speed of sound, for optimum engine efficiency and vehicle speed. There are few or no moving parts, but achieving proper ignition and combustion in a matter of milliseconds proved to be an engineering challenge of the highest order. After a series of successful wind tunnel tests, however, NASA is ready to prove that air-breathing scramjets work in flight.

This will mark the first time a non-rocket, air-breathing scramjet engine has powered a vehicle in flight at hypersonic speeds, defined as speeds above Mach 5 or five times the speed of sound.

Researchers believe these technologies may someday offer more airplane-like operations and other benefits compared to traditional rocket systems. Rockets provide limited throttle control and must carry heavy tanks filled with liquid oxygen, necessary for combustion of fuel. An air-breathing engine, like that on the X-43A, scoops oxygen from the air as it flies. The weight savings could be used to increase payload capacity, increase range or reduce vehicle size for the same payload.

The X-43A will fly in the Naval Air Warfare Center Weapons Division Sea Range over the Pacific Ocean off the coast of southern California.

After booster burnout, the 2,800-pound, wedge-shaped research vehicle will separate and fly on its own to perform a preprogrammed set of tasks. After an approximate ten second test firing of the engine, the X-43A will glide through the atmosphere conducting a series of aerodynamic maneuvers for up to six minutes on its way to splashdown.

This will be the second flight in the X-43A project. On June 2, 2001, the first X-43A vehicle was lost moments after release from the wing of the B-52. Following booster ignition, the combined booster and X-43A vehicle deviated from its flight path and was deliberately destroyed. Investigation into the mishap showed that there was no single contributing factor, but the root cause of the problem was identified as the control system of the booster.

For this flight, the B-52 will carry the booster with the attached X-43A to at least 40,000 feet before its release, versus the 24,000 feet of the first attempt. The booster will carry the X-43A research vehicle to approximately the same test conditions -- altitude and speed -- as planned for the first flight.

NASA's Langley Research Center, Hampton, Va., and Dryden Flight Research Center, Edwards, Calif., jointly conduct the Hyper-X program.

A video clip, images and additional information about the project are available on the Internet at:

http://www.nasa.gov/missions/research/x43-main.html

NASA Television will carry the flight and the post-flight news briefing live. NASA TV is available on AMC 9, TRANSPONDER 9C, 85 degrees west longitude, vertical polarization with a frequency of 3880 MHz and audio of 6.8 MHz.